Process for bonding thermoplastic materials



, Jan. 3, 1950 F. J. DOFSEN ET AL 2,492,973

PROCESS FOR BONDING THERMOPLASTIC MATERIALS Filed July 15, 1947 2Sheets-Sheet 1 I I 1 l I Ff JNVENTORS {7 EL L-DANlE-IljON BY FLOYDJ-DOEITSEN ATTORNEYS Jan.3, 1950 M. DOFSEN AL 2 49mm PROCESS .FORBONDING THERMOPLASTIC MATERIALS Filed July 15, 19467 2 Sheets-Sheet 2INVENTORS ELMEr'Q L DANIELSON BY FLOYD J. DoFsEN AT I'ORINEYS M,MH M

Patented Jan. 3, 1950 i e .7 irnocnss :Fon BONDING wnEnMor-msrrw:

v r v MATERIALS Floyd J- ,D fs n, Mame .andlslhner rt. Danielson,Oakland, Calif,

Animation July 115, 1947, Serial No. 761,128

3 Glaims. (01.18 59) 1 An Ohififit of our invention is to carry out aiil ess of bonding thermoplastic materials to l roviide a productconsisting of two or more oi the-materials whose sole connection to eachother is the bond, The materials may .be .of different.

colors.

A further object of our inventiori' is to provide a. process .ot bondingthermoplastic materials where one loi the thermoplastics is precast andhesurface'which is tohe bonded to the second thermoplastic material iscoated with a solvent, whereupon (the coated precast material is placedin a. mold thatis to receive the second injection of 'i7h.ermoplas ticmaterial, and the second-mate rial'willihecome bonded to the first.T-Ilhe precast material may form the top of ,a key and have slotstherein defining the character on the key,

The apparatus tor carryin out the proces permits the premoldi-ng of aplurality of the fir t articles and the subsequent melding ofthe sec--ond thermoplastic material to all of theprecast art cles simultaneously.thereby greatly speeding.

uprthe manufacture of the twoema erialm ---Other obiects-and advantageswill appear in the zfiollowingrspecification, :and thetnovel features ofthe-devioewil1tbe particularly pointed outi theappendedclaims.

Onr invention is illustrated in the accompanyingidmw'ings forming a partofthis application; 1

in which:

Figure 1 is a perspective view ofth'e lower rnold" 01' a setofir'n'oldsand'showing the precast or premoldedrmemhers in a position toreceive the solvent and then to be dropped into the recesses provided inthe-lower mold;

Figure 2 is an enlarged transverse section of the lower mold taken alongthe line IIII of Figure 1 and further illustrates the upper mold inposition and the second thermoplastic matearticles formed of the twothermoplastic mater rials;

figure? is a, top plan view ojjligure 6'; Figure 8-'is a verticalsection on an enlarged scale of one of the articles shown in Figure 7;

2 Ensure -.9 is a bottom plansviem off'c hi miek' shown in Eigurofl; end

,Fligure :10 is an isometric viewottho-lcomnlfloi article;

While we have shown only themrmwrm: of our invention, it shouldlbemndccsioosl -sthst: various changes ormediflcati m more within thescope-of the departing from the spirit and sc pe; Qf; invention. l

In carrying outourimventlmi; W ipm: lower mold indicated generally-atand :-this mold has a p urality: annuities A plurality of PreQfizSirey'lfineer cousins-mm- I or wear. tacits :13 are shown comectedsten-2, by branchs nues .3. mhespnncsstocethervmthw said ringer pi c s havingbeen-merhusiynmsost: in the term of wafers ztherlnoplattic-;-.zn,e.-t e--v rial 2a separate mold, not shown Inmdditlon to the iSDlU-BS 12 ands,:fee 'ins lhrzonchlsnrrmsnzin the-shape of a lead to the sortie-251cm nentral: branch spru da also connects wlththe ammizs. e ranch sprues 4'and-4e; constitutes-a; which permi s the opera onto :hold. k y p n aposition nirectly-labovertiiemwms mold-cavities I which itey-;are'tc.zpe.- mmcd. Thisis clearly shown .iniigure t1. 7 A solvent,such as acetone, is alim fi i :io under suniacesfi of :the :keycanssohsito sol-tab these surfaces to an.-;apnr eiahlernenth=.. caps; rethen sev re vtromsthe; hunch and will dropr-hy gravityl-imzo-lthecmolshcmtiqc l. Since there are two mwsnf-mtlsi; trated inFigur '-1 there w'tldze-twmemuns maker: ap po tioned above thesecavities-sand; their reariaces havetbeen sottencd ihylmeans, e nim; he hysaepsnh'hoth-smups evered from theirhraneh smilesand-willedmi into theott ms oflthe on1: hoth;

This Tarr n ementspeeds hpithe lnrccess alumnu rear If aces nor, in theseverin rof makeu -ms; he branch sprit s :3 and he simphlnenmhemiinw themold-cavities. The parti ular icenstructionmi'. caps is shown in,Figures ;3, 4mm! .5. Waldo-amt wish to e confined to ayipaticuler-fshane that he precast -thermoplasticanemberzh trfllftailre,be-. cause conntless art cles may he: zinmedlm thermoplastic materialsand can be bound together in the same manner. The key caps shown inFigures 1 to 5, inclusive, and the completed keys shown in Figures 6 to10, inclusive, are only set forth as one example of how our process canmanufacture a group of articles simultaneously. The outer face 6 of thekey cap B is shown in Figure 5 and the face has a slot 1 formed thereinin the shape of ,a core, such as the number 5. The under face 5' of thekey cap is indicated in Figure 3 and it will be seen that a recess 9 isformed in the rear face that communicates with the slot 1 thus providinga surrounding margin on this face of the cap. A reinforcing rib l mayextend across the recess and integral projections I I may be arranged atthe four corners of the recess for the purpose of providing a moreperfect bond between the precast key cap and the remainder of the key.

In Figure 2 the lower mold A is shown with its cavities 1 receiving the,key caps B, which are placed in an inverted position in the bottoms ofthe cavities. As already stated, the rear faces 5 of the key caps havehad a solvent, such as acetone, applied thereto to soften the rearsurfaces to an appreciable depth. The upper mold C is now placed overthe lower mold and the upper mold carries core members 12 that enter thecavities l for causing the second injection of thermoplastic material toform the body of a key of the desired shape and structure. The secondmaterial will be bonded to the cap.

- The-upper mold has a longitudinally extending groove 13 that willreceive the second thermoplastic material and branch grooves l4extending from the central groove will convey the material to the moldcavities l. The injection of the second thermoplastic material willcause this material to fill the cavity spaces not occupied by the keycaps and the core members. A portion of the second thermoplasticmaterial will flow under pressure into the recess 9 and will fill theslotl. The second material is preferably of a different color from thatof the first so that the material filling the slots 1 will formcharacters that will be in striking contrast to the color of the outersurface of the'key cap.

Figure 6 illustrates the group of completed articles removed from thelower and upper molds with the keys D still connected to the centralsprue 15 by branch sprues IS. The second material forming the bodyofeach key cap will be perfectly and permanently bonded to the firstmaterial forming the finger piece thereof, due to the fact'tha't' theinjection of the second material underpressure has taken place while thesolvent has softened. the rear face of the finger piece to anappreciable depth. It is a simple matter to break off the completed keysfrom the branch spruesand thesecaps will take the shape of that shown inFigures 8, 9 and 10. The rear faces 5 of the-key caps B will be bondedto the keys D along their entire abutting surfaces.

'The'core I2 is shaped so that the second thermoplastic material willform a socket I! in the cap D for receiving a key shank'indicated by thedot dash line at l8 (Fig.8). The socket I1 is spaced from the innersurfaces of the key by ribs [9 and these ribs act as reinforcing membersfor the key socket. There will be no wear noticeable on the key=oap fromuse on an adding or multiplying machine or the like, because the number5 for example shown in Figure 5, will have a depth of material equal tothe entire thickness of the finger engaging piece or wear facing. The

entire key cap will therefore have to wear away before the characterwill disappear.

We claim:

1. In the herein described process of molding at least two thermoplasticmaterials together to form a key cap, the steps of precasting athermoplastic face member having a character perforation therethrough,providing a' hollow key mold set with the base thereof extendingdownwardly, applying a solvent to the under surface of the face memberto soften it, dropping said face member in an inverted position into thebottom of the mold, and injectin under pressure a second thermoplasticmaterial into the face member perforation and body cavity of the mold tointerfuse with the softened face member and effect a permanent bondtherewith.

4 2. The method of molding two thermoplastic materials of differentcolor together to form a key cap comprising a body and a facemember onone end thereof, consisting of preforming a plurality of thermoplasticcap face members! interconnected by a sprue and each having a characterslot therein, treating the lower surfaces of said face members with asolvent to soften them, providing inverted cap body molds, severing saidcaps from the sprue and dropping them into the bottom of said invertedbody molds with their lower surfaces uppermost therein, filling saidmolds and the face members with a second thermoplastic material underpressure to form characters in the slots of the face members and formthe body portions of the several caps, said second material interfusingwith the softened cap surfaces to bond the parts of each cap into ahomogeneous mass.

3. The method of molding a finger piece .for computing machine keysconsisting in first molding the finger engaging face portion thereof inthe form of a wafer of thermoplastic material of a given color having anunder marginal edge and a central throughway opening depicting a keycharacter, applying a solvent to the lower surface of said wafer,providing a mold for the body of the finger piece, placing the wafer ininverted position in one end of the mold and introducing into the otherend of said mold thermoplastic material of a contrasting color underpressure to force it into the character opening of the face of the waferand into union with the under marl gin of the wafer.

FLOYD J. DOFSEN.

ELMER L. DANIELSON.

REFERENCES CITED The following references file of this patent:

UNITED STATES PATENTS are of record in the Great Britain May 10, 1940

